Desktop,Cli: Import: Fix video files are not imported as resources

[personalizedrefrigerator]

Summary

Fixes an issue in which <video src="./path/to/file"> did not result in ./path/to/file being imported as a resource (as it would be for <imgs and <as).

Important

Joplin is still unable to render the imported video files, as <video src=":/someresourceid"> markup seems to currently be unsupported. For videos to play, it seems to currently be necessary to convert imported HTML to Markdown, then manually replace the <video tags with [resource links].

It may make sense to add support for rendering videos from local resources in this or a follow-up pull request.

Partially resolves #13549.

Testing

1. Import "Procédure.one" from the test file provided in Fix issues with import of OneNote files #13549.
2. Verify that the video in "Tuto vidéo - partage Carnet de notes Joplin" has a resource URL.
3. Convert the note to Markdown.
4. Replace the <video controls src=":/..."> with a [resource link](:/...).
5. Verify that the video renders below the link and can be played.

[personalizedrefrigerator]

Closing for now — imported video files don't export correctly (or render in the note viewer). More work will need to be done before this change is ready for review/merge.